The present invention relates to anti-microbial activity of the essential oil of Cymbopogon flexuosus (Nees ex Steud.) Wats and the process of isolation of novel sesquiterpene compound mainly responsible for the strong anti-microbial/anti-bacterial activity. The present invention particularly relates to anti-bacterial activity of the essential oil and a pure isolate identified as (+)-1-bisabolone of formula 1 against gram positive bacteria from a strain of a grass identified as Cymbopogon flexuosus. 
Cymbopgon species (family Poaceae) arc native to tropical and subtropical regions of Asia and Africa. The aromatic grasses such as Cymbopogon and Vetiveria zizanioides have been known because of their medicinal and perfumery values. The genus Cymbopogon is well known source of aroma chemicals especially terpenoids. Essential oil derived from Cymbopogon species such as Java citronella (Cymbopogon winterianus), Palmarosa (Cymbopogon martini var. motia) and Lemongrass (Cymbopogon flexuosus) are very popular and widely consumed in the world market. The chemical compounds present in varying concentrations in the species, varieties, ecotypes and chemotypes of the Cymbopogon grass have a great demand due to their uses in perfumery, flavour and pharmaceutical industry. There are approximately sixty species of Cymbopogon native to tropical and subtropical regions of Africa and Asia. (Corrigan, D 1992, in xe2x80x9cAdverse Effects of Herbal Drugsxe2x80x9d Vol. 1, Springer verlag, Berlin, 115-123). Out of twenty seven species available in India mainly Cymbopogon flexuosus, C.winterianus and C.martini var. motia have been exploited for commercial cultivation as a source of citral, citronellal and geraniol respectively.
Development of the new chemocultivars having the higher percentage of essential oils is generally carried out by the method of phenotypic mass selection. The oil obtained from the elite stain of Cymbopogon flexuosus, described herein, RLJCF (HSR) is rich in (+)-1-bisabolone of formula 1 (30-50%) which owing to strong UV absorption at 224 nm and refreshing flowery note including potent anti-bacterial properties may find extensive use in sun-screen lotions, creams and related preparations as well as in the antiseptic and deodorizing preparations such as creams, after shave lotions, sprays and powders.
There are a few reports of the occurrence of (xe2x88x92)-1-bisabolone from a natural source. The first report of its presence (15%) in Stevia purpurea Pers was made by F. Bohlmann et al. (F. Bohlmann, C. Zedro and S. Schonewiess, Chem. Ber. 109, 1976, 3366-3370). Another publication reporting its presence (12%) in Ethopian Cymbopogon citratus. (B. Abegaz, P. G. Yohaunes and R. K. Dieter, Jour. Nat. Prod. 46, 1983, 424-426). Melkani et al. also reported the enantiomer (xe2x88x92)-1-bisabolone in concentration ranging from 18-68% In one of the oils of two varieties of Cymbopogon distans (A. B. Melkani, P. Joshi, A. K. Pant, C. S. Mathela and Vasudev, Jour. Nat. Prod. 48, 1985, 995-997).
The main object of the present invention is to unravel the potent anti-bacterial activity of main constiutent (+)-1-bisabolone preset in the volatile oil of the locally developed and grown plant Cymbopogon flexuosus, named RLJCF(HSR).
From a detailed scrutiny of the published literature it is apparent that the presence of (+)-1-bisabolone from a natural source has not been reported earlier. Therefore, the presence of (+)-1-bisabolone from Cymbopogon flexuosus being the first report, is novel and the anti-bacterial activity of the oil bearing the active compound is also novel.
Accordingly the present invention relates to a novel sesquiterpene, (+)-1-bisabolone of the formula 1 given below 
The present invention also relates to a process for the isolation of a novel sesquiterpene, (+)-1-bisabolone of the formula 1 from Cymbopogon flexuosus 
said process comprising hydrodistilling freshly harvested leaves of the grass Cymbopogon flexuosus, extracting the distillate with a non-polar solvent to obtain a concentrate, further hydrodistilling the obtained concentrate and separating the essential oil, followed by separating of the sesquiterpene of formula 1 from the essential oil.
In one embodiment of the invention, the non-polar solvent used for extraction of the distillate is selected from the group consisting of n-hexane, petroleum ether and dichloromethane.
In one embodiment of the invention, the sesquiterpene of the formula 1 is separated from the essential oil using column chromatography.
In yet another embodiment of the invention, the yield of (+)-1-bisabolone of formula 1 from Cymbopogon flexuosus essential oil is 35-45%.
In another embodiment of the invention, the (+)-1-bisabolone of formula 1 possesses in vitro anti-microbial activity against gram positive bacteria selected from Bacillus cereus, Staphylococcus aureus and Bacillus subtilis. 
In another embodiment of the invention, the sesquiterpene of the formula 1 is separated from the essential oil using fractionation.
The present invention also relates to an essential oil obtained form the freshly harvested leaves of Cymbopogon flexuosus and containing a sesquiterpene (+)-1-bisabolone as the active ingredient, said essential oil being anti-bacterial activity against gram positive bacteria.
In another embodiment of the invention, the yield of (+)-1-bisabolone rich oil from Cymbopogon flexuosus is 0.3-0.4%.
In another embodiment of the invention, the essential oil possesses in vitro anti-microbial activity against gram-positive bacteria selected from Bacillus cereus, Staphylococcus aureus and Bacillus subtilis.